Max Fleischer

: : It became
widely known when Mitch Miller's TV program "Sing Along with Mitch" was popular.
I'm not sure Mitch and his crew originated it, though.

: Wasn't this sing-a-long
bouncing ball a feature of early movies too?

"A popular attraction of early
motion picture exhibition were the Sing Alongs. In between pictures, the house
organist would play a popular song of the day and the audience would be invited
to sing along. If they didn't know the words it was ok because they would be shown
on screen through the use of slides. Between 1924 and 1925, the idea came up within
the Fleischer Studios to place these words on to film. That was a fair idea in
it's self, but it was decided to take this thought a step further and also provided
some guidance (as to what to sing and when) for the audience. They eventually
came to the idea of bouncing a 'ball' over the word that was to be sung in its
proper place in the song."